Multi-level envelope tracking systems with adjusted voltage steps

ABSTRACT

Multi-level envelope tracking systems with adjusted voltage steps are provided. In certain embodiments, an envelope tracking system for generating a power amplifier supply voltage for a power amplifier is provided. The envelope tracking system includes a multi-level supply (MLS) DC-to-DC converter that outputs multiple regulated voltages, an MLS modulator that controls selection of the regulated voltages over time based on an envelope signal corresponding to an envelope of a radio frequency (RF) signal amplified by the power amplifier, and a modulator output filter coupled between an output of the MLS modulator and the power amplifier supply voltage. The envelope tracking system further includes a switching point adaptation circuit configured to control the voltage level of the regulated voltages outputted by the MLS DC-to-DC converter based on a power level of the RF signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/948,550, filed Sep. 23, 2020, and titled “MULTI-LEVEL ENVELOPETRACKING SYSTEMS WITH ADJUSTED VOLTAGE STEPS,” which claims the benefitof priority under 35 U.S.C. § 119 of U.S. Provisional Patent ApplicationNo. 62/906,932, filed Sep. 27, 2019 and titled “MULTI-LEVEL ENVELOPETRACKING SYSTEMS WITH ADJUSTED VOLTAGE STEPS,” which is hereinincorporated by reference in its entirety.

BACKGROUND Field

Embodiments of the invention relate to electronic systems, and inparticular, to power amplifiers for radio frequency (RF) electronics.

Description of the Related Technology

Power amplifiers are used in RF communication systems to amplify RFsignals for transmission via antennas. It is important to manage thepower of RF signal transmissions to prolong battery life and/or providea suitable transmit power level.

Examples of RF communication systems with one or more power amplifiersinclude, but are not limited to, mobile phones, tablets, base stations,network access points, customer-premises equipment (CPE), laptops, andwearable electronics. For example, in wireless devices that communicateusing a cellular standard, a wireless local area network (WLAN)standard, and/or any other suitable communication standard, a poweramplifier can be used for RF signal amplification. An RF signal can havea frequency in the range of about 30 kHz to 300 GHz, such as in therange of about 410 MHz to about 7.125 GHz for fifth generation (5G)communications in frequency range 1 (FR1).

SUMMARY

In certain embodiments, the present disclosure relates to an envelopetracking system. The envelope tracking system includes a power amplifierconfigured to amplify a radio frequency signal and to receive power froma power amplifier supply voltage, and an envelope tracker configured togenerate the power amplifier supply voltage based on an envelope signalcorresponding to an envelope of the radio frequency signal. The envelopetracker includes a DC-to-DC converter configured to output a pluralityof regulated voltages, a modulator configured to control the poweramplifier supply voltage based on the plurality of regulated voltagesand the envelope signal, and a switching point adaptation circuitconfigured to control a voltage level of at least one of the pluralityof regulated voltages based on a power level of the radio frequencysignal.

In some embodiments, the switching point adaptation circuit isconfigured to control the voltage level of each of the plurality ofregulated voltages based on the power level of the radio frequencysignal.

In various embodiments, the switching point adaptation circuit includesa power estimation circuit configured to estimate the power level of theradio frequency signal based on a signal power value for or at least oneof a transmit frame or a transmit symbol. According to a number ofembodiments, the signal power value indicates an average power for thetransmit frame or symbol. In accordance with several embodiments, thesignal power value indicates a peak power for the transmit frame orsymbol. According to some embodiments, the switching point adaptationcircuit further includes a voltage estimation circuit configured toestimate a plurality of desired voltage levels associated with thesignal power value. In accordance with a number of embodiments, theswitching point adaptation circuit further includes a programmingcircuit configured to control the DC-to-DC converter to output theplurality of regulated voltages each with a corresponding one of theplurality of desired voltage levels.

In several embodiments, the envelope tracking system further includestwo or more power amplifiers configured to amplify two or more radiofrequency signals, the envelope tracker including two or more modulatorseach configured to receive the plurality of regulated voltages and toprovide modulation to generate a supply voltage for a corresponding oneof the two or more power amplifiers. According to a number ofembodiments, the switching point adaptation circuit is configured tocontrol the voltage level based on a largest power level of the two ormore radio frequency signals.

In several embodiments, the DC-to-DC converter is configured to receivea battery voltage, and to generate the plurality of regulated voltagesbased on providing DC-to-DC conversion of the battery voltage.

In some embodiments, each of the plurality of regulated voltages has adifferent voltage level.

In various embodiments, the envelope tracker further includes aplurality of decoupling capacitors each coupled between ground and acorresponding one of the plurality of regulated voltages.

In a number of embodiments, the modulator includes a plurality ofswitches each coupled between the modulator output voltage and acorresponding one of the plurality of regulated voltages.

In several embodiments, the envelope tracker further includes amodulator output filter connected between an output of the modulator andthe power amplifier supply voltage, the modulator output filterincluding at least one series inductor and at least one shunt capacitor.

In certain embodiments, the present disclosure relates to a mobiledevice. The mobile device includes a transceiver configured to generatea radio frequency transmit signal, a front end circuit including a poweramplifier configured to amplify the radio frequency transmit signal andto receive power from a power amplifier supply voltage, and a powermanagement circuit including an envelope tracker configured to generatethe power amplifier supply voltage based on an envelope signalcorresponding to an envelope of the radio frequency transmit signal. Theenvelope tracker includes a DC-to-DC converter configured to output aplurality of regulated voltages, a modulator configured to control thepower amplifier supply voltage based on the plurality of regulatedvoltages and the envelope signal, and a switching point adaptationcircuit configured to control a voltage level of at least one of theplurality of regulated voltages based on a power level of the radiofrequency transmit signal.

In various embodiments, the switching point adaptation circuit isconfigured to control the voltage level of each of the plurality ofregulated voltages based on the power level of the radio frequencytransmit signal.

In some embodiments, the switching point adaptation circuit includes apower estimation circuit configured to estimate the power level of theradio frequency transmit signal based on a signal power value for atleast one of a transmit frame or a transmit symbol. According to anumber of embodiments, the signal power value indicates an average powerfor the transmit frame or symbol. In accordance with variousembodiments, the signal power value indicates a peak power for thetransmit frame or symbol. According to several embodiments, theswitching point adaptation circuit further includes a voltage estimationcircuit configured to estimate a plurality of desired voltage levelsassociated with the signal power value. In accordance with a number ofembodiments, the switching point adaptation circuit further includes aprogramming circuit configured to control the DC-to-DC converter tooutput the plurality of regulated voltages each with a corresponding oneof the plurality of desired voltage levels.

In several embodiments, the mobile device further includes two or morepower amplifiers configured to amplify two or more radio frequencytransmit signals, the envelope tracker including two or more modulatorseach configured to receive the plurality of regulated voltages and toprovide modulation to generate a supply voltage for a corresponding oneof the two or more power amplifiers. According to various embodiments,the switching point adaptation circuit is configured to control thevoltage level based on a largest power level of the two or more radiofrequency transmit signals.

In some embodiments, the DC-to-DC converter is configured to receive abattery voltage, and to generate the plurality of regulated voltagesbased on providing DC-to-DC conversion of the battery voltage.

In various embodiments, each of the plurality of regulated voltages hasa different voltage level.

In several embodiments, the envelope tracker further includes aplurality of decoupling capacitors each coupled between ground and acorresponding one of the plurality of regulated voltages.

In some embodiments, the modulator includes a plurality of switches eachcoupled between the modulator output voltage and a corresponding one ofthe plurality of regulated voltages.

In various embodiments, mobile device further includes a modulatoroutput filter connected between an output of the modulator and the poweramplifier supply voltage, the modulator output filter including at leastone series inductor and at least one shunt capacitor.

In certain embodiments, the present disclosure relates to a method ofenvelope tracking. The method includes amplifying a radio frequencysignal using a power amplifier, supplying power to the power amplifierusing a power amplifier supply voltage, outputting a plurality ofregulated voltages from a DC-to-DC converter, and controlling the poweramplifier supply voltage based on the plurality of regulated voltagesand an envelope signal using a modulator, the envelope signalcorresponding to an envelope of the radio frequency signal. The methodfurther includes controlling a voltage level of at least one of theplurality of regulated voltages based on a power level of the radiofrequency signal.

In various embodiments, the method further includes controlling each ofthe plurality of regulated voltages based on the power level of theradio frequency signal.

In some embodiments, the method further includes estimating the powerlevel of the radio frequency signal based on a signal power value for atleast one of a transmit frame or a transmit symbol. According to anumber of embodiments, the signal power value indicates an average powerfor the transmit frame or symbol. In accordance with severalembodiments, the signal power value indicates a peak power for thetransmit frame or symbol. According to various embodiment, the methodfurther includes estimating a plurality of desired voltage levelsassociated with the signal power value. In accordance with severalembodiments, the method further includes controlling the DC-to-DCconverter to output the plurality of regulated voltages each with acorresponding one of the plurality of desired voltage levels.

In several embodiments, the method further includes generating theplurality of regulated voltages based on providing DC-to-DC conversionof a battery voltage.

In various embodiments, each of the plurality of regulated voltages hasa different voltage level.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a mobile device according to oneembodiment.

FIG. 2 is a schematic diagram of one embodiment of an envelope trackingsystem for a power amplifier.

FIG. 3A is a schematic diagram of another embodiment of an envelopetracking system.

FIG. 3B is a schematic diagram of another embodiment of an envelopetracking system.

FIG. 4 is a graph of voltage versus time for five examples of signalwaveforms of different power levels.

FIG. 5A is a graph of one example of power amplifier supply voltageversus input power.

FIG. 5B is a graph of one example of power added efficiency (PAE) versusoutput power for various examples of signal waveforms.

FIG. 6A is a graph of another example of power amplifier supply voltageversus input power.

FIG. 6B is a graph of another example of PAE versus output power forvarious examples of signal waveforms.

FIG. 7 is a schematic diagram of a mobile device according to anotherembodiment.

FIG. 8 is a schematic diagram of one embodiment of a communicationsystem for transmitting radio frequency (RF) signals.

FIG. 9 is a schematic diagram of a multi-level supply (MLS) modulationsystem according to one embodiment.

FIG. 10 is a schematic diagram of an MLS DC-to-DC converter according toone embodiment.

FIG. 11 is a schematic diagram of one example of timing for MLS DC-to-DCconversion.

FIG. 12 is a schematic diagram of one example of MLS envelope trackingfor a continuous wave signal.

DETAILED DESCRIPTION OF EMBODIMENTS

The following detailed description of certain embodiments presentsvarious descriptions of specific embodiments. However, the innovationsdescribed herein can be embodied in a multitude of different ways, forexample, as defined and covered by the claims. In this description,reference is made to the drawings where like reference numerals canindicate identical or functionally similar elements. It will beunderstood that elements illustrated in the figures are not necessarilydrawn to scale. Moreover, it will be understood that certain embodimentscan include more elements than illustrated in a drawing and/or a subsetof the elements illustrated in a drawing. Further, some embodiments canincorporate any suitable combination of features from two or moredrawings.

Envelope tracking is a technique that can be used to increase poweradded efficiency (PAE) of a power amplifier by efficiently controlling avoltage level of a power amplifier supply voltage in relation to anenvelope of a radio frequency (RF) signal amplified by the poweramplifier. Thus, when the envelope of the RF signal increases, thevoltage supplied to the power amplifier can be increased. Likewise, whenthe envelope of the RF signal decreases, the voltage supplied to thepower amplifier can be decreased to reduce power consumption.

Envelope tracking can include applications in which the envelope signalfollows the fast changing instantaneous power of the RF signal. In otherapplications, the envelope signal can be much slower, for instance,determined by a longer time average of the RF signal. For example, whenusing symbol by symbol tracking, the envelope signal changes relativelyinfrequently in comparison to the fast varying instantaneous power of anorthogonal frequency division multiplexing (OFDM) signal. For instance,for a 5G OFDM waveform instantaneous power can change between peaks andtroughs in less than 10 ns, while symbols can change every 16 us. Incertain implementations, the envelope signal can be based upon the nextoncoming peak of the RF signal, thus anticipating rather than followingthe RF power.

Multi-level envelope tracking systems with adjusted voltage steps areprovided. In certain embodiments, an envelope tracking system forgenerating a power amplifier supply voltage for a power amplifier isprovided. The envelope tracking system includes an MLS DC-to-DCconverter that outputs multiple regulated voltages, an MLS modulatorthat controls selection of the regulated voltages over time based on anenvelope signal corresponding to an envelope of the RF signal amplifiedby the power amplifier, and a modulator output filter coupled between anoutput of the MLS modulator and the power amplifier supply voltage. Theenvelope tracking system further includes a switching point adaptationcircuit configured to control the voltage level of the regulatedvoltages outputted by the MLS DC-to-DC converter based on a power levelof the RF signal.

By controlling the voltage level of the regulated voltages based on thepower level of the RF signal, enhanced efficiency can be achieved. Forexample, the switching point of the MLS DC-to-DC converter can beadapted based on the RF signal's power level to provide a predictiveadjustment of the regulated voltages to thereby increase efficiency overa wide range of signal powers.

In certain implementations, the switching point adaptation circuitcontrols the regulated voltages outputted by the MLS DC-to-DC converterbased on a signal power value indicated for a particular transmissionslot or frame. For instance, in certain systems, an amount of averageand/or peak signal power can be known before a transmission slot orframe (for instance, instructed by a base station of a communicationnetwork), and thus can be used to control the voltage levels of theregulated voltages.

Improved performance of a multi-level envelope tracking system can beachieved by adapting the discrete voltage level scale to suitablevoltage levels (for instance, minimum and maximum voltage values)corresponding to the signal power (for instance, average power) setduring the transmitted burst or frame. Such tracking can be done for awide range of transmission scenarios, including, but not limited to,time-division duplexing (TDD).

Accordingly, in certain implementations power amplifier supply voltagecan be controlled based on the expected peak power for the next burst orframe, or even adjusted dynamically during the transmission. Bycontrolling the regulated voltages in this manner, a size of the voltagesteps selected can be decreased to allow for finer tracking of thevoltage on the power amplifier.

For instance, prior to the beginning of a transmission, the peak toaverage and the average power are known and this knowledge allows forthe calculation of the maximum and minimum voltage desired. In certainimplementations, decoupling capacitors holding charge for each of theregulated voltages of the MLS DC-to-DC converter can be pre-charged tothe corresponding voltages.

By implementing an envelope tracking system in this manner, enhancedprecision of envelope tracking can be achieved over a wide range ofsignal power, including, at back off or when operating high and low peakto average.

In certain implementations, the envelope tracking system operates as apower supply capable of switching between multiple voltages to supply apower amplifier through a baseband filter. The power supply iscontrolled to generate a number of different voltages that are static orfixed compared to the modulation bandwidth of the amplitude of the RFsignal waveform through the power amplifier. Additionally, the regulatedvoltages are adapted to a power demand (for instance, an average power)of the power amplifier.

In certain implementations, the regulated voltages from the MLS DC-to-DCconverter are processed by two or more MLS modulators to generate thepower amplifier supply voltages of two or more power amplifiers. Forinstance, carrier aggregation systems, multi-input multiple-output(MIMO) systems, and/or other communications systems can operate using ashared MLS DC-to-DC converter. In certain implementations, the switchingpoint adaptation circuit controls the regulated voltages based on thelargest signal power amplified by the power amplifiers.

For instance, in the case of MIMO or carrier aggregation, where multiplepower amplifier paths operate simultaneously, the envelope trackingsystem can select the voltage scale appropriate to the power amplifiercarrying the most power. This advantageously allows for reduced powerconsumption by adapting voltages for the highest power consuming branchfirst. In certain applications, it can be advantageous to set a fixedsupply to one power amplifier by using a single modulator switchposition for one power amplifier and allowing the other voltages to beused by the modulator for the second power amplifier.

In certain implementations, a digital pre-distortion (DPD) systempre-calculates voltage settings and pre-distorts the RF based on theknowledge of the power amplifier supply voltage (Vcc) filtercharacteristics and a calibration of the power amplifier response.

FIG. 1 is a schematic diagram of a mobile device 70 according to oneembodiment. The mobile device 70 includes a primary antenna 1, adiversity antenna 2, a primary antenna tuning circuit 3, a diversityantenna tuning circuit 4, a double-pole double-throw (DPDT) antennadiversity switch 5, a primary front end module 6, a diversity front endmodule 7, a battery 8, an MLS envelope tracker 9, a transceiver 10, abaseband modem 11, and an application processor 12.

Although one embodiment of a mobile device is shown, the teachingsherein are applicable to mobile devices implemented in a wide variety ofways. Accordingly, other implementations are possible.

In the illustrated embodiment, the primary front end module 6 includes afirst power amplifier 21, a second power amplifier 22, a third poweramplifier 23, a fourth power amplifier 24, a first low noise amplifier31, a second low noise amplifier 32, a third low noise amplifier 33, adiplexer 42, a transmit/receive band switch 41, a transmit filter 43, afirst duplexer 45, a second duplexer 46, a third duplexer 47, a firstreceive filter 51, a second receive filter 52, a third receive filter53, a first directional coupler 59, and a second directional coupler 60.Additionally, the diversity front end module 7 includes a first lownoise amplifier 35, a second low noise amplifier 36, a first receivefilter 55, a second receive filter 56, a first receive band selectionswitch 61, and a second receive band selection switch 62.

Although one embodiment of front end circuitry is shown, otherimplementations of front end circuitry are possible. For instance, frontend circuitry can include power amplifiers (PAs), low noise amplifiers(LNAs), filters, switches, phase shifters, duplexers, and/or othersuitable circuitry for processing RF signals transmitted and/or receivedfrom one or more antennas. Example functionalities of a front endinclude but are not limited to, amplifying signals for transmission,amplifying received signals, filtering signals, switching betweendifferent bands, switching between different power modes, switchingbetween transmission and receiving modes, duplexing of signals,multiplexing of signals (for instance, diplexing or triplexing), or somecombination thereof.

Accordingly, other implementations of primary front end modules,diversity receive front end modules, antenna selection, and/or antennatuning can be used.

As shown in FIG. 1, the MLS envelope tracker 9 is used to generate oneor more power amplifier supply voltages for power amplifiers used in themobile device 70 to amplify RF signals for wireless transmission. In theillustrated embodiment, the MLS envelope tracker 9 receives a batteryvoltage V_(BATT) from the battery 8, and generates a first poweramplifier supply voltage V_(PA1) for the first power amplifier 21 and asecond power amplifier supply voltage V_(PA2) for the first poweramplifier 22. Although an example in which the MLS envelope tracker 9generates two power amplifier supply voltages is shown, the MLS envelopetracker 9 can generate more or fewer power amplifier supply voltages.

The MLS envelope tracker 9 controls the first power amplifier supplyvoltage V_(PA1) to track an envelope of a first RF signal amplified bythe first power amplifier 21. Additionally, the MLS envelope tracker 9controls the second power amplifier supply voltage V_(PA2) to track anenvelope of a second RF signal amplified by the second power amplifier22. In certain implementations, the MLS envelope tracker 9 receives oneor more envelope signals from the baseband modem 11. For example, theMLS envelope tracker 9 can receive a first envelope signal indicating anenvelope of the first RF signal and a second envelope signal indicatingan envelope of the second RF signal. The envelope signal(s) can beanalog or digital.

The battery 8 can be any suitable battery for use in the mobile device70, including, for example, a lithium-ion battery. The battery voltageV_(BATT) is regulated by a DC-to-DC converter of the MLS envelopetracker 9 to generate regulated voltages used for multi-level envelopetracking in accordance with the teachings herein.

The transceiver 10 generates RF signals for transmission and processesincoming RF signals received from the primary antenna 1 and thediversity antenna 2. It will be understood that various functionalitiesassociated with the transmission and receiving of RF signals can beachieved by one or more components that are collectively represented inFIG. 1 as the transceiver 10. In one example, separate components (forinstance, separate circuits or dies) can be provided for handlingcertain types of RF signals.

The baseband modem 11 provides the transceiver 10 with digitalrepresentations of transmit signals, which the transceiver 10 processesto generate RF signals for transmission. The baseband modem 11 alsoprocesses digital representations of received signals provided by thetransceiver 10.

As shown in FIG. 1, the baseband modem 11 is coupled to the applicationprocessor 12, which serves to provide primary application processing inthe mobile device 70. The application processor 12 can provide a widevariety of functions, such as providing system capabilities suitable forsupporting applications, including, but not limited to, memorymanagement, graphics processing, and/or multimedia decoding.

Although the mobile device 70 illustrates one example of an RF systemincluding a multi-level envelope tracker, a wide variety of RF systemscan include a multi-level envelope tracker implemented in accordancewith the teachings herein.

FIGS. 2-3B depict schematic diagram of various embodiments of envelopetracking systems for a power amplifier. However, the teachings hereinare applicable to envelope trackers implemented in a wide variety ofways. Accordingly, other implementations are possible.

FIG. 2 is a schematic diagram of one embodiment of an envelope trackingsystem 100 for a power amplifier 71. The envelope tracking system 100includes an MLS DC-to-DC converter 72, a switching point adaptationcircuit 75, an MLS modulator 81, and a modulator output filter 91. TheMLS DC-to-DC converter 72 is also referred to herein as a switchingregulator.

The power amplifier 71 amplifies an RF input signal RF_(IN) to generatean RF output signal RF_(OUT). The MLS modulator 81 receives an envelopesignal (ENVELOPE), which changes in relation to an envelope of the RFinput signal RF_(IN).

In the illustrated embodiment, the MLS DC-to-DC converter 72 receives abattery voltage V_(BATT), and provides DC-to-DC conversion to generate avariety of regulated voltages V_(MLSa), V_(MLSb), V_(MLSc) . . .V_(MLSn) of different voltage levels. Although an example in which fourMLS voltages is depicted, the MLS DC-to-DC converter 72 can generatemore or fewer MLS voltages as indicated by the ellipses.

The MLS modulator 81 receives the regulated voltages V_(MLSa), V_(MLSb),V_(MLSc) . . . V_(MLSn) and the envelope signal, and provides amodulator output voltage to the modulator output filter 91. In certainimplementations, the MLS modulator 81 controls the outputted voltagebased on selecting a suitable regulated voltage over time based on theenvelope signal. For example, the MLS modulator 81 can include a bank ofswitches for selectively connecting the regulated voltages V_(MLSa),V_(MLSb), V_(MLSc) . . . V_(MLSn) to the modulator's output based on avalue of the envelope signal.

The modulator output filter 91 filters the output of MLS modulator 81 tothereby generate a power amplifier supply voltage V_(PA) for the poweramplifier 71.

As shown in FIG. 2, the envelope tracking system 100 also includes theswitching point adaptation circuit 75, which controls the voltage levelsof one or more of the regulated voltages V_(MLSa), V_(MLSb), V_(MLSc) .. . V_(MLSn) based on a power level of the RF signal RF_(IN). In certainimplementations, the switching point adaptation circuit 75 controlspulse widths of the MLS DC-to-DC converter 72 used for regulation (see,for example, FIG. 11), thereby controlling the switching points ofregulation and the corresponding regulated voltage levels.

By controlling the voltage levels of the regulated voltages V_(MLSa),V_(MLSb), V_(MLSc) . . . V_(MLSn) based on a power level of the RFsignal RF_(IN), enhanced efficiency can be achieved. For example, theswitching point of the MLS DC-to-DC converter 72 can be adapted based onthe RF signal's power level, thereby allowing a predictive adjustment ofthe regulated voltages to thereby increase efficiency over a wide rangeof signal powers.

In certain implementations, the switching point adaptation circuit 75controls the voltage levels of the regulated voltages V_(MLSa),V_(MLSb), V_(MLSc) . . . V_(MLSn) based on an amount of transmit powerindicated in a transmit frame or slot. For example, the switching pointadaptation circuit 75 can receive data indicating the amount of transmitpower from a baseband modem or other suitable source.

The envelope tracking system 100 is well-suited for applications usingsymbol by symbol tracking, which can be suitable for high bandwidthmodulations. For example, when using symbol by symbol tracking, two MLSvoltages can be programmed and used in succession at the symbol rate(for instance, 16 us in 5G). Thus, the MLS modulator 81 can change thevoltage used for generating the power amplifier supply voltage byswitching to the new voltage holding capacitor.

FIG. 3A is a schematic diagram of another embodiment of an envelopetracking system 150 for a power amplifier module 101. The envelopetracking system 150 includes an envelope tracking integrated circuit(IC) 102, a modulator output filter 104, envelope shaping circuitry 105,envelope signal conditioning circuitry 106, a switching point adaptationcircuit 109, first to fourth decoupling capacitors 111-114,respectively, and an inductor 117.

Although one embodiment of an envelope tracking system is shown in FIG.3A, the teachings herein are applicable to envelope tracking systemsimplemented in a wide variety of ways. Accordingly, otherimplementations are possible.

In the illustrated embodiment, the envelope tracking IC 102 includes MLSswitching circuitry 121, a digital control circuit 122, a baseband MLSmodulator 123, and a modulator control circuit 124. The envelopetracking IC 102 of FIG. 3A is depicted with various pins or pads forproviding a variety of functions, such as receiving a battery voltage(V_(BATT)), receiving switching point adaptation data from the switchingpoint adaptation circuit 109, communicating over a serial peripheralinterface (SPI), receiving an envelope signal (ENVELOPE), connecting tothe decoupling capacitors 111-114, and connecting to the inductor 117.An envelope tracking IC is also referred to herein in as an envelopetracking semiconductor die or chip.

The MLS switching circuitry 121 controls a current through the inductor117 to provide voltage regulation. For example, the MLS switchingcircuitry 121 can include switches and a controller that turns on andoff the switches using any suitable regulation scheme (including, butnot limited to, pulse-width modulation) to provide DC-to-DC conversion.In the illustrated embodiment, the MLS switching circuitry 121 outputsfour regulated MLS voltages of different voltage levels. However, theMLS switching circuitry 121 can be implemented to output more or fewerregulated voltages.

As shown in FIG. 3A, the MLS switching circuitry 121 is controlled bythe digital control circuit 122. The digital control circuit 122 canprovide programmability to the MLS switching circuitry 121, the MLSmodulator 123, and/or the modulator control circuit 124. As shown inFIG. 3A, the digital control circuit 122 is coupled to the SPI bus. Incertain implementations, the digital control circuit 122 controls theMLS switching circuitry 121, the MLS modulator 123, and/or the modulatorcontrol circuit 124 based on data received over the SPI bus and/or otherchip interface.

The baseband MLS modulator 123 includes an output coupled to the poweramplifier supply voltage V_(PA) through the modulator output filter 104.In certain implementations, the baseband MLS modulator 123 includesswitches coupled between each of the regulated MLS voltages and themodulator output filter 104. Additionally, the modulator's switches areselectively opened or closed by the modulator controller 124 based onthe envelope signal.

In the illustrated embodiment, the modulator output filter 104 includesa first series inductor 127, a second series inductor 128, a first shuntcapacitor 125, and a second shunt capacitor 126. Although an exampleimplementation of a modulator output filter is depicted in FIG. 3A, theteachings herein are applicable to modulator output filter filtersimplemented in a wide variety of ways. Accordingly, otherimplementations of filters can be used in accordance with the teachingsherein.

In certain implementations, one or more components of a filter arecontrollable (for instance, digitally programmable and/or analog-tuned)to provide enhanced flexibility and/or configurability. For example, inthe illustrated embodiment, the first shunt capacitor 125 and the secondshunt capacitor 126 have capacitance values that are controllable.Although two examples of controllable filter components are shown, otherfilter components can additionally or alternatively be implemented to becontrollable.

In the illustrated embodiment, the power amplifier module 101 includes apower amplifier 107 and supply voltage filter 108. The supply voltagefilter 108 includes a series inductor 133, a first shunt capacitor 131,and a second shunt capacitor 132. Although one implementation of a poweramplifier module is shown, the teachings herein are applicable to poweramplifier modules implemented in a wide variety of ways. Accordingly,other implementations are possible.

As shown in FIG. 3A, the switching point adaptation circuit 109 includesa power estimation circuit 141, a voltage estimation circuit 142, and anMLS programming circuit 143. The power estimation circuit 141 operatesto estimate a signal power of the RF signal RF_(IN). In certainimplementations, the power estimation circuit 141 receives digital dataindicating a signal power associated with a particular transmit frame orslot.

The voltage estimation circuit 142 operates to estimate desired voltagelevels of one or more of the regulated output voltages of the MLSswitching circuitry 121 based on the estimated power. The MLSprogramming circuit 143 operates to program the MLS switching circuitry121 based on the estimated voltage. In the illustrated embodiment, theMLS switching circuitry 121 is programmed over a separate interface fromthe SPI bus. In another embodiment, the switching point adaptationcircuit 109 programs the MLS switching circuitry 121 over the SPI busand/or other common interface to the envelope tracking IC 102.

Although one embodiment of a switching point adaptation circuit isshown, the teachings herein are applicable to switching point adaptationcircuits implemented in a wide variety of ways.

FIG. 3B is a schematic diagram of another embodiment of an envelopetracking system 160. The envelope tracking system 160 includes anenvelope tracking IC 152, a first modulator output filter 104 a, asecond modulator output filter 104 b, first envelope shaping circuitry105 a, second envelope shaping circuitry 105 b, first envelope signalconditioning circuitry 106 a, second envelope signal conditioningcircuitry 106 b, a switching point adaptation circuit 109, first tofourth decoupling capacitors 111-114, respectively, and an inductor 117.The envelope tracking system 160 generates a first power amplifiersupply voltage V_(PA1) for the first power amplifier module 101 a, and asecond power amplifier supply voltage V_(PA2) for the second poweramplifier module 101 b.

In the illustrated embodiment, the envelope tracking IC 152 includes MLSswitching circuitry 121, a digital control circuit 122, a first basebandMLS modulator 123 a, a second baseband MLS modulator 123 b, a firstmodulator control circuit 124 a, and a second modulator control circuit124 b.

The envelope tracking system 160 of FIG. 3B is similar to the envelopetracking system 150 of FIG. 3A, except that the envelope tracking system160 illustrates one implementation in which a common or shared MLSDC-to-DC converter is used in combination with multiple modulators togenerate multiple power amplifier supply voltages.

In certain implementations, the regulated voltages from an MLS DC-to-DCconverter are processed by two or more MLS modulators to generate thepower amplifier supply voltages of two or more power amplifiers. Incertain implementations, the switching point adaptation circuit controlsthe regulated voltages based on the largest signal power amplified bythe power amplifiers.

FIG. 4 is a graph of voltage versus time for five examples of signalwaveforms of different power levels. The illustrated example is depictedfor MCS0 20 MHz WLAN waveforms of five levels, with 30 MHz power supplyfilter bandwidth.

As shown in FIG. 4, the 5 voltage levels in this example are set basedon the amplitude of the signal such that the minimum and maximum of thevoltage levels match those of the time varying waveform. For example,FIG. 4 depicts for 5 different average powers, 5 different voltagescales that track a pulse of amplitude versus time.

FIG. 5A is a graph of one example of power amplifier supply voltageversus input power. The example shows a voltage scale for 24 dBm ofpower without an adapted voltage table. Voltage steps are between 1.7 Vand 5.5 V, with 5.5 V corresponding to maximum peak power of 35 dBm,satisfying 30.5 dBm average output power for a typical LTE waveform.

FIG. 5B is a graph of one example of power added efficiency (PAE) versusoutput power for various examples of signal waveforms.

A single voltage is chosen for each power on the x axis, resulting in anefficiency curve selected for a given voltage at each power. Thecombination of the single voltages chosen for each power draws a jaggedoverlaid efficiency curve, which represents the realizable poweramplifier efficiency for the system.

The example shows results for various waveforms, with a power amplifierefficiency average at 24 dBm of about 35%.

FIG. 6A is a graph of another example of power amplifier supply voltageversus input power. The example shows a voltage scale for 24 dBm ofpower with one example of an adapted voltage steps. Voltage steps arebetween 1.7 V and 2.7 V, with 2.7 V corresponding to max peak power of28.5 dBm, satisfying 24 dBm average output power for a typical LTEwaveform.

FIG. 6B is a graph of another example of PAE versus output power forvarious examples of signal waveforms. The example shows results forvarious waveforms, with a power amplifier efficiency average at 24 dBmof about 42%. This is a significant improvement over the 35% efficiencynumber associated with FIG. 5B. By selecting lower voltages preciselyadapted to the 24 dBm average transmit power, the realizable poweramplifier efficiency is significantly improved.

FIG. 7 is a schematic diagram of a mobile device 800 according toanother embodiment. The mobile device 800 includes a baseband system801, a transceiver 802, a front end system 803, antennas 804, a powermanagement system 805, a memory 806, a user interface 807, and a battery808.

The mobile device 800 can be used communicate using a wide variety ofcommunications technologies, including, but not limited to, 2G, 3G, 4G(including LTE, LTE-Advanced, and LTE-Advanced Pro), 5G, WLAN (forinstance, Wi-Fi), WPAN (for instance, Bluetooth and ZigBee), WMAN (forinstance, WiMax), and/or GPS technologies.

The transceiver 802 generates RF signals for transmission and processesincoming RF signals received from the antennas 804. It will beunderstood that various functionalities associated with the transmissionand receiving of RF signals can be achieved by one or more componentsthat are collectively represented in FIG. 7 as the transceiver 802. Inone example, separate components (for instance, separate circuits ordies) can be provided for handling certain types of RF signals.

The front end system 803 aids is conditioning signals transmitted toand/or received from the antennas 804. In the illustrated embodiment,the front end system 803 includes power amplifiers (PAs) 811, low noiseamplifiers (LNAs) 812, filters 813, switches 814, and duplexers 815.However, other implementations are possible.

For example, the front end system 803 can provide a number offunctionalizes, including, but not limited to, amplifying signals fortransmission, amplifying received signals, filtering signals, switchingbetween different bands, switching between different power modes,switching between transmission and receiving modes, duplexing ofsignals, multiplexing of signals (for instance, diplexing ortriplexing), or some combination thereof.

In certain implementations, the mobile device 800 supports carrieraggregation, thereby providing flexibility to increase peak data rates.Carrier aggregation can be used for both Frequency Division Duplexing(FDD) and Time Division Duplexing (TDD), and may be used to aggregate aplurality of carriers or channels. Carrier aggregation includescontiguous aggregation, in which contiguous carriers within the sameoperating frequency band are aggregated. Carrier aggregation can also benon-contiguous, and can include carriers separated in frequency within acommon band or in different bands.

The antennas 804 can include antennas used for a wide variety of typesof communications. For example, the antennas 804 can include antennasassociated transmitting and/or receiving signals associated with a widevariety of frequencies and communications standards.

In certain implementations, the antennas 804 support MIMO communicationsand/or switched diversity communications. For example, MIMOcommunications use multiple antennas for communicating multiple datastreams over a single radio frequency channel. MIMO communicationsbenefit from higher signal to noise ratio, improved coding, and/orreduced signal interference due to spatial multiplexing differences ofthe radio environment. Switched diversity refers to communications inwhich a particular antenna is selected for operation at a particulartime. For example, a switch can be used to select a particular antennafrom a group of antennas based on a variety of factors, such as anobserved bit error rate and/or a signal strength indicator.

The mobile device 800 can operate with beamforming in certainimplementations. For example, the front end system 803 can include phaseshifters having variable phase controlled by the transceiver 802.Additionally, the phase shifters are controlled to provide beamformation and directivity for transmission and/or reception of signalsusing the antennas 804. For example, in the context of signaltransmission, the phases of the transmit signals provided to theantennas 804 are controlled such that radiated signals from the antennas804 combine using constructive and destructive interference to generatean aggregate transmit signal exhibiting beam-like qualities with moresignal strength propagating in a given direction. In the context ofsignal reception, the phases are controlled such that more signal energyis received when the signal is arriving to the antennas 804 from aparticular direction. In certain implementations, the antennas 804include one or more arrays of antenna elements to enhance beamforming.

The baseband system 801 is coupled to the user interface 807 tofacilitate processing of various user input and output (I/O), such asvoice and data. The baseband system 801 provides the transceiver 802with digital representations of transmit signals, which the transceiver802 processes to generate RF signals for transmission. The basebandsystem 801 also processes digital representations of received signalsprovided by the transceiver 802. As shown in FIG. 7, the baseband system801 is coupled to the memory 806 of facilitate operation of the mobiledevice 800.

The memory 806 can be used for a wide variety of purposes, such asstoring data and/or instructions to facilitate the operation of themobile device 800 and/or to provide storage of user information.

The power management system 805 provides a number of power managementfunctions of the mobile device 800. The power management system 805 caninclude an MLS envelope tracker 860 implemented in accordance with oneor more features of the present disclosure.

As shown in FIG. 7, the power management system 805 receives a batteryvoltage form the battery 808. The battery 808 can be any suitablebattery for use in the mobile device 800, including, for example, alithium-ion battery.

FIG. 8 is a schematic diagram of one embodiment of a communicationsystem 950 for transmitting RF signals. The communication system 950includes a battery 901, an MLS envelope tracker 902, a power amplifier903, a directional coupler 904, a duplexing and switching circuit 905,an antenna 906, a baseband processor 907, a signal delay circuit 908, adigital pre-distortion (DPD) circuit 909, an I/Q modulator 910, anobservation receiver 911, an intermodulation detection circuit 912, anenvelope delay circuit 921, a coordinate rotation digital computation(CORDIC) circuit 922, a shaping circuit 923, a digital-to-analogconverter 924, and a reconstruction filter 925.

The communication system 950 of FIG. 8 illustrates one example of an RFsystem that can include an envelope tracking system implemented inaccordance with one or more features of the present disclosure. However,the teachings herein are applicable to RF systems implemented in a widevariety of ways.

The baseband processor 907 operates to generate an in-phase (I) signaland a quadrature-phase (Q) signal, which correspond to signal componentsof a sinusoidal wave or signal of a desired amplitude, frequency, andphase. For example, the I signal and the Q signal provide an equivalentrepresentation of the sinusoidal wave. In certain implementations, the Iand Q signals are outputted in a digital format. The baseband processor907 can be any suitable processor for processing baseband signals. Forinstance, the baseband processor 907 can include a digital signalprocessor, a microprocessor, a programmable core, or any combinationthereof.

The signal delay circuit 908 provides adjustable delay to the I and Qsignals to aid in controlling relative alignment between thedifferential envelope signal ENV_p, ENV_n provided to the MLS envelopetracker 902 and the RF signal RF_(IN) provided to the power amplifier903. The amount of delay provided by the signal delay circuit 908 iscontrolled based on amount of intermodulation in adjacent bands detectedby the intermodulation detection circuit 912.

The DPD circuit 909 operates to provide digital shaping to the delayed Iand Q signals from the signal delay circuit 908 to generate digitallypre-distorted I and Q signals.

In the illustrated embodiment, the DPD provided by the DPD circuit 909is controlled based on amount of intermodulation detected by theintermodulation detection circuit 912. The DPD circuit 909 serves toreduce a distortion of the power amplifier 903 and/or to increase theefficiency of the power amplifier 903.

The I/Q modulator 910 receives the digitally pre-distorted I and Qsignals, which are processed to generate the RF signal RF_(IN). Forexample, the I/Q modulator 910 can include DACs configured to convertthe digitally pre-distorted I and Q signals into an analog format,mixers for upconverting the analog I and Q signals to radio frequency,and a signal combiner for combining the upconverted I and Q signals intothe RF signal RF_(IN). In certain implementations, the I/Q modulator 910can include one or more filters configured to filter frequency contentof signals processed therein.

The envelope delay circuit 921 delays the I and Q signals from thebaseband processor 907. Additionally, the CORDIC circuit 922 processesthe delayed I and Q signals to generate a digital envelope signalrepresenting an envelope of the RF signal RF_(IN). Although FIG. 8illustrates an implementation using the CORDIC circuit 922, an envelopesignal can be obtained in other ways.

The shaping circuit 923 operates to shape the digital envelope signal toenhance the performance of the communication system 950. In certainimplementations, the shaping circuit 923 includes a shaping table thatmaps each level of the digital envelope signal to a corresponding shapedenvelope signal level. Envelope shaping can aid in controllinglinearity, distortion, and/or efficiency of the power amplifier 903.

In the illustrated embodiment, the shaped envelope signal is a digitalsignal that is converted by the DAC 924 to a differential analogenvelope signal. Additionally, the differential analog envelope signalis filtered by the reconstruction filter 925 to generate a differentialenvelope signal ENV_p, ENV_n suitable for use by a differential envelopeamplifier of the MLS envelope tracker 902. In certain implementations,the reconstruction filter 925 includes a differential low pass filter.

Although one example of envelope signaling is shown, the teachingsherein are applicable to envelope signaling implemented in a widevariety of ways. For instance, in another example, the DAC 924 and thereconstruction filter 925 are omitted in favor of providing the MLSenvelope tracker 902 with digital envelope data.

With continuing reference to FIG. 8, the MLS envelope tracker 902receives the envelope signal from the reconstruction filter 925 and abattery voltage V_(BATT) from the battery 901, and uses the differentialenvelope signal ENV_p, ENV_n to generate a power amplifier supplyvoltage V_(CC_PA) for the power amplifier 903 that changes in relationto the envelope of the RF signal RF_(IN). The power amplifier 903receives the RF signal RF_(IN) from the I/Q modulator 910, and providesan amplified RF signal RF_(OUT) to the antenna 906 through the duplexingand switching circuit 905, in this example.

The directional coupler 904 is positioned between the output of thepower amplifier 903 and the input of the duplexing and switching circuit905, thereby allowing a measurement of output power of the poweramplifier 903 that does not include insertion loss of the duplexing andswitching circuit 905. The sensed output signal from the directionalcoupler 904 is provided to the observation receiver 911, which caninclude mixers for providing down conversion to generate downconverted Iand Q signals, and DACs for generating I and Q observation signals fromthe downconverted I and Q signals.

The intermodulation detection circuit 912 determines an intermodulationproduct between the I and Q observation signals and the I and Q signalsfrom the baseband processor 907. Additionally, the intermodulationdetection circuit 912 controls the DPD provided by the DPD circuit 909and/or a delay of the signal delay circuit 908 to control relativealignment between the differential envelope signal ENV_p, ENV_n and theRF signal RF_(IN). In another embodiment, the intermodulation detectioncircuit 912 additionally or alternatively controls a delay of the signaldelay circuit 921.

By including a feedback path from the output of the power amplifier 903and baseband, the I and Q signals can be dynamically adjusted tooptimize the operation of the communication system 950. For example,configuring the communication system 950 in this manner can aid inproviding power control, compensating for transmitter impairments,and/or in performing DPD.

Although illustrated as a single stage, the power amplifier 903 caninclude one or more stages. Furthermore, the teachings herein areapplicable to communication systems including multiple power amplifiers.

FIG. 9 is a schematic diagram of an MLS modulation system 1050 accordingto one embodiment. The MLS modulation system 1050 includes a modulatorcontrol circuit 1020, an MLS DC-to-DC converter 1025, a modulator switchbank 1027, and a decoupling capacitor bank 1030.

The MLS modulation system 1050 of FIG. 9 illustrates one implementationof MLS modulator circuitry suitable for incorporation in a multi-levelenvelope tracker. However, other implementations of MLS modulatorcircuitry can be included in multi-level envelope trackers implementedin accordance with the teachings herein.

The MLS DC-to-DC converter 1025 generates a first regulated voltageV_(MLS1), a second regulated voltage V_(MLS2), and a third regulatedvoltage V_(MLS3) based on providing DC-to-DC conversion of a batteryvoltage V_(BATT). Although an example with three regulated voltages isshown, the MLS DC-to-DC converter 1025 can generate more or fewerregulated voltages. In certain implementations, at least a portion ofthe regulated voltages are boosted relative to the battery voltageV_(BATT). Additionally or alternatively, one or more of the regulatedvoltages is a buck voltage having a voltage lower than the batteryvoltage V_(BATT).

The decoupling capacitor bank 1030 aids in stabilizing the regulatedvoltages generated by the MLS DC-to-DC converter 1025. For example, thedecoupling capacitor bank 1030 of FIG. 9 includes a first decouplingcapacitor 1031 for decoupling the first regulated voltage V_(MLS1), asecond decoupling capacitor 1032 for decoupling the second regulatedvoltage V_(MLS2), and a third decoupling capacitor 1033 for decouplingthe third regulated voltage V_(MLS3).

With continuing reference to FIG. 9, the modulator switch bank 1027includes a first switch 1041 connected between the modulator's output(MOD_(OUT)) and the first regulated voltage V_(MLS) 1, a second switch1042 connected between the modulator's output and the second regulatedvoltage V_(MLS2), and a third switch 1043 connected between themodulator's output and the third regulated voltage V_(MLS3). Themodulator control 1020 operates to selectively open or close theswitches 1041-1043 to thereby control modulator's output.

FIG. 10 is a schematic diagram of an MLS DC-to-DC converter 1073according to one embodiment. The MLS DC-to-DC converter 1073 includes aninductor 1075, a first switch S₁, a second switch S₂, a third switch S₃,a fourth switch S₄, a fifth switch S₅, and a sixth switch S₆. The MLSDC-to-DC converter 1073 further includes control circuitry (not shown inFIG. 10) for opening and closing the switches to provide regulation.

The MLS DC-to-DC converter 1073 of FIG. 10 illustrates oneimplementation of an MLS DC-to-DC converter suitable for incorporationin a multi-level envelope tracker. However, other implementations of MLSDC-to-DC converters can be included in multi-level envelope trackersimplemented in accordance with the teachings herein.

In the illustrated embodiment, the first switch S₁ includes a first endelectrically connected to the battery voltage V_(BATT) and a second endelectrically connected to a first end of the second switch S₂ and to afirst end of the inductor 1075. The second switch S₂ further includes asecond end electrically connected to a first or ground supply V_(GND).Although FIG. 10 illustrates a configuration of a DC-to-DC converterthat is powered using a ground supply and a battery voltage, theteachings herein are applicable to DC-to-DC converters powered using anysuitable power supplies. The inductor 1075 further includes a second endelectrically connected to a first end of each of the third to sixthswitches S₃-S₆. The third switch S₃ further includes a second endelectrically connected to the ground supply V_(GND). The fourth, fifth,and sixth switches S₄-S₆ each include a second end configured togenerate the first, second, and third regulated voltages V_(MLS1),V_(MLS2), and V_(MLS3), respectively.

The first to sixth switches S₁-S₆ are selectively opened or closed tomaintain regulated voltages within a particular error tolerance oftarget voltage levels. Although an example with three regulated voltagesis shown, the MLS DC-to-DC converter 1073 can be implemented to generatemore or fewer regulated voltages.

In the illustrated embodiment, the MLS DC-to-DC converter 1073 operatesas a buck-boost converter operable to generate regulated boost voltagesgreater than the battery voltage V_(BATT) and/or regulated buck voltageslower than the battery voltage V_(BATT). However, other implementationsare possible.

FIG. 11 is a schematic diagram of one example of timing for MLS DC-to-DCconversion. As shown in FIG. 11, the width of regulation cycles can beused to control the voltage level of the regulated voltages generated byMLS DC-to-DC conversion. For instance, one MLS regulated voltage can beassociated with a period t1, while a second regulation voltage can beassociated with a different period t2. Additionally, a non-overlapperiod tovlp can be used to avoid crowbar currents between differentvoltage levels.

In certain implementations herein, one or more regulation periods (forinstance, t1 and/or t2) and/or one or more non-overlap period (forinstance, tovlop) are digitally controllable. In certainimplementations, the delays are controlled based on a digital statemachine and/or other suitable circuitry.

The regulated voltages generated by MLS DC-to-DC conversion can beselectively provided by a modulator to a modulator output filter. In theillustrated example, the modulator output filter is depicted asincluding shunt capacitors C1 and C2 and series inductors L1 and L2.However, other implementations of modulator output filters are possible.

FIG. 12 is a schematic diagram of one example of MLS envelope trackingfor a continuous wave signal. The example shown is for a continuous wavesignal having a frequency of about 100 MHz and a corresponding period ofabout 10 ns. Examples of suitable MLS voltage levels for the signal areshown.

CONCLUSION

Some of the embodiments described above have provided examples inconnection with mobile devices. However, the principles and advantagesof the embodiments can be used for any other systems or apparatus thathave needs for envelope tracking.

Unless the context clearly requires otherwise, throughout thedescription and the claims, the words “comprise,” “comprising,” and thelike are to be construed in an inclusive sense, as opposed to anexclusive or exhaustive sense; that is to say, in the sense of“including, but not limited to.” The word “coupled”, as generally usedherein, refers to two or more elements that may be either directlyconnected, or connected by way of one or more intermediate elements.Likewise, the word “connected”, as generally used herein, refers to twoor more elements that may be either directly connected, or connected byway of one or more intermediate elements. Additionally, the words“herein,” “above,” “below,” and words of similar import, when used inthis application, shall refer to this application as a whole and not toany particular portions of this application. Where the context permits,words in the above Detailed Description using the singular or pluralnumber may also include the plural or singular number respectively. Theword “or” in reference to a list of two or more items, that word coversall of the following interpretations of the word: any of the items inthe list, all of the items in the list, and any combination of the itemsin the list.

Moreover, conditional language used herein, such as, among others,“can,” “could,” “might,” “can,” “e.g.,” “for example,” “such as” and thelike, unless specifically stated otherwise, or otherwise understoodwithin the context as used, is generally intended to convey that certainembodiments include, while other embodiments do not include, certainfeatures, elements and/or states. Thus, such conditional language is notgenerally intended to imply that features, elements and/or states are inany way required for one or more embodiments or that one or moreembodiments necessarily include logic for deciding, with or withoutauthor input or prompting, whether these features, elements and/orstates are included or are to be performed in any particular embodiment.

The above detailed description of embodiments of the invention is notintended to be exhaustive or to limit the invention to the precise formdisclosed above. While specific embodiments of, and examples for, theinvention are described above for illustrative purposes, variousequivalent modifications are possible within the scope of the invention,as those skilled in the relevant art will recognize. For example, whileprocesses or blocks are presented in a given order, alternativeembodiments may perform routines having steps, or employ systems havingblocks, in a different order, and some processes or blocks may bedeleted, moved, added, subdivided, combined, and/or modified. Each ofthese processes or blocks may be implemented in a variety of differentways. Also, while processes or blocks are at times shown as beingperformed in series, these processes or blocks may instead be performedin parallel, or may be performed at different times.

The teachings of the invention provided herein can be applied to othersystems, not necessarily the system described above. The elements andacts of the various embodiments described above can be combined toprovide further embodiments.

While certain embodiments of the inventions have been described, theseembodiments have been presented by way of example only, and are notintended to limit the scope of the disclosure. Indeed, the novel methodsand systems described herein may be embodied in a variety of otherforms; furthermore, various omissions, substitutions and changes in theform of the methods and systems described herein may be made withoutdeparting from the spirit of the disclosure. The accompanying claims andtheir equivalents are intended to cover such forms or modifications aswould fall within the scope and spirit of the disclosure.

What is claimed is:
 1. An envelope tracking system comprising: a poweramplifier configured to amplify a radio frequency signal and to receivepower from a power amplifier supply voltage; and an envelope trackerconfigured to provide the power amplifier supply voltage at an envelopetracker output, the envelope tracker including a DC-to-DC converterconfigured to output a plurality of regulated voltages, a switchingpoint adaptation circuit configured to control a voltage level of atleast one of the plurality of regulated voltages based on a power levelof the radio frequency signal, a modulator including a plurality ofswitches each coupled between the envelope tracker output and acorresponding one of the plurality of regulated voltages, and amodulator control circuit configured to control activation of theplurality of switches based on an envelope of the radio frequencysignal.
 2. The envelope tracking system of claim 1 wherein the switchingpoint adaptation circuit is configured to control the voltage level ofeach of the plurality of regulated voltages based on the power level ofthe radio frequency signal.
 3. The envelope tracking system of claim 1wherein the switching point adaptation circuit includes a powerestimation circuit configured to estimate the power level of the radiofrequency signal based on a signal power value for a transmit frame. 4.The envelope tracking system of claim 3 wherein the signal power valueindicates an average power.
 5. The envelope tracking system of claim 3wherein the signal power value indicates a peak power.
 6. The envelopetracking system of claim 3 wherein the switching point adaptationcircuit further includes a voltage estimation circuit configured toestimate a plurality of desired voltage levels associated with thesignal power value.
 7. The envelope tracking system of claim 6 whereinthe switching point adaptation circuit further includes a programmingcircuit configured to control the DC-to-DC converter to output theplurality of regulated voltages each with a corresponding one of theplurality of desired voltage levels.
 8. The envelope tracking system ofclaim 1 wherein the switching point adaptation circuit includes a powerestimation circuit configured to estimate the power level of the radiofrequency signal based on a signal power value for a transmit symbol. 9.The envelope tracking system of claim 1 wherein each of the plurality ofregulated voltages has a different voltage level.
 10. The envelopetracking system of claim 1 further comprising a modulator output filtercoupled to the envelope tracker output and configured to filer the poweramplifier supply voltage.
 11. A mobile device comprising: a transceiverconfigured to generate a radio frequency signal for transmission; afront end circuit including a power amplifier configured to amplify theradio frequency signal and to receive power from a power amplifiersupply voltage; and a power management circuit including an envelopetracker configured to provide the power amplifier supply voltage at anenvelope tracker output, the envelope tracker including a DC-to-DCconverter configured to output a plurality of regulated voltages, aswitching point adaptation circuit configured to control a voltage levelof at least one of the plurality of regulated voltages based on a powerlevel of the radio frequency signal, a modulator including a pluralityof switches each coupled between the envelope tracker output and acorresponding one of the plurality of regulated voltages, and amodulator control circuit configured to control activation of theplurality of switches based on an envelope of the radio frequencysignal.
 12. The mobile device of claim 11 wherein the switching pointadaptation circuit includes a power estimation circuit configured toestimate the power level of the radio frequency transmit signal based ona signal power value for a transmit frame.
 13. The mobile device ofclaim 12 wherein the switching point adaptation circuit further includesa voltage estimation circuit configured to estimate a plurality ofdesired voltage levels associated with the signal power value.
 14. Themobile device of claim 13 wherein the switching point adaptation circuitfurther includes a programming circuit configured to control theDC-to-DC converter to output the plurality of regulated voltages eachwith a corresponding one of the plurality of desired voltage levels. 15.The mobile device of claim 11 wherein the envelope tracker furtherincludes a modulator output filter coupled to the envelope trackeroutput and configured to filer the power amplifier supply voltage. 16.The mobile device of claim 11 wherein each of the plurality of regulatedvoltages has a different voltage level.
 17. A method of envelopetracking, the method comprising: amplifying a radio frequency signalusing a power amplifier; supplying power to the power amplifier using apower amplifier supply voltage from an envelope tracker output of anenvelope tracker; generating a plurality of regulated voltages using aDC-to-DC converter of the envelope tracker; controlling a voltage levelof at least one of the plurality of regulated voltages based on a powerlevel of the radio frequency signal using a switching point adaptationcircuit of the envelope tracker; and controlling activation of aplurality of switches of a modulator of the envelope tracker based on anenvelope of the radio frequency signal, the plurality of switches eachcoupled between the envelope tracker output and a corresponding one ofthe plurality of regulated voltages.
 18. The method of claim 17 furthercomprising estimating the power level of the radio frequency signalbased on a signal power value for a transmit frame, and estimating aplurality of desired voltage levels associated with the signal powervalue.
 19. The method of claim 17 further comprising filtering the poweramplifier supply voltage using a modulator output filter coupled to theenvelope tracker output.
 20. The method of claim 17 wherein each of theplurality of regulated voltages has a different voltage level.